Liquid crystal display elements are advantaged over other display elements in terms of its thin thickness, light weight, and low power consumption. The liquid crystal display elements are widely used in image display apparatuses such as televisions, video cassette recorders, and the like, and OA (Office Automation) apparatuses such as monitors, word processors, personal computers, and the like.
Conventionally known liquid crystal display methods of the liquid crystal display elements are, for example, the TN (Twisted Nematic) mode in which a nematic liquid crystal is used, display modes in which FLC (Ferroelectric Liquid crystal) or AFLC (Antiferroelectric Liquid crystal) is used, a polymer dispersion type liquid crystal display mode, and the like mode.
Among the liquid crystal display methods, for example, the TN (Twisted Nematic) mode in which the nematic liquid crystal is used is conventionally adopted in the liquid crystal display elements in practical use. The liquid crystal display elements using the TN mode have disadvantages of slow response, narrow viewing angle, and similar drawbacks. Those disadvantages are large hindrances for the TN mode to overtake the CRT (Cathode Ray Tube).
Moreover, the display modes in which the FLC or AFLC is used, are advantageous in their fast response and wide viewing angles, but significantly poor in anti-shock property and temperature characteristics. Therefore, the display modes in which the FLC or AFLC is used, have not been widely used practically.
Further, the polymer dispersion type liquid crystal display mode, which utilizes scattering of light, does not need polarization and is capable of performing highly bright display. However, in principle, the polymer dispersion type liquid crystal display mode cannot control the viewing angle by using a phase plate (retardation film). Further, the polymer dispersion type liquid crystal display mode has a problem in terms of its response property. Thus, the polymer dispersion type liquid crystal display mode is not so advantageous over the TN mode.
In all those display methods, liquid crystal molecules are oriented in a certain direction and thus a displayed image looks differently depending on an angle between a line of vision and the liquid crystal molecules. On this account, all those display methods have viewing angle limits. Moreover, all the display methods utilize rotation of the liquid crystal molecules, the rotation caused by application of an electric field on the liquid crystal molecules. Because the liquid crystal molecules are rotated in alignment all together, responses take time in all the display method. Note that the display modes in which the FLC and the AFLC are used, are advantageous in the response speed and the viewing angle, but have such a problem that their alignment would be irreversibly destroyed by an external force.
In contrast to those display methods in which the rotation of the molecules by the application of the electric field is utilized, a display method in which the secondary electro-optical effect is utilized.
The electro-optical effect is a phenomenon in which a refractive index of a material is changed by an external electric field. There are two types of electro-optical effect: one is an effect proportional to the electric field and the other is proportional to the square of the electric field. The former is called the Pockels effect and the latter is called the Kerr effect. Especially the Kerr effect has been adopted in high-speed optical shutters early on, and has been practically used in a special measurement instruments. The Kerr effect was discovered by J. Kerr in 1875. So far, organic liquid such as nitrobenzene, carbon disulfide, and the like, are known as material showing the Kerr effect. Those materials are used, for example, in the aforementioned optical shutters, and similar devices. Further, those materials are used for measurement of strength of high electric fields for power cables and the like.
Later on, it was found that liquid crystal materials have a large Kerr constant. Research has been performed using the large Kerr constant of the liquid crystal materials for use in light modulation devices, light deflection devices, and further optical integrated circuit. It was reported that some liquid crystal compounds have a Kerr constant more than 200 times higher than that of nitrobenzene.
Under those circumstances, studies for utilization of the Kerr effect in display apparatuses has been started. It is expected that the utilization of the Kerr effect attains a relatively low voltage driving because the Kerr effect is proportional to the square of the electric field. Further, it is expected that the utilization of the Kerr effect attains a high-response display apparatus because the Kerr effect shows a response property of several μ seconds to several m seconds, as its basic nature.
Under there circumstances, for instance, Patent publication 1 (Publication of Japanese Patent Application, publication No. 2001-249363 (Tokukai 2001-249363; published on Sep. 14, 2001)), Patent publication 2 (Publication of Japanese Patent Application, publication No. 11-183937 (Tokukaihei 11-183937; published on Jul. 9, 1999); corresponding to U.S. Pat. No. 6,266,109), and non-Patent publication 1 (Shiro MATSUMOTO et al “Fine droplets of liquid crystals in a transparent polymer and their response to an electric field”, Appl. Phys. Lett., 1996, Vol. 69, p. 1044-1046) suggest display elements in which a medium made from a liquid crystalline material is sealed between a pair of substrates and the Kerr effect is induced by application of an electric field parallel or perpendicular to the substrates.
Such display elements are provided with polarizers on respective outer sides of the substrates, the polarizers having absorption axes cross each other perpendicularly. When no electric field (voltage) is applied, the medium is optically isotropic and thus the display element displays black. When a electric field (voltage) is applied, birefringence occurs thereby changing transmissivity to perform gray scale display. With this arrangement, it is possible to realize very high contrast along a normal direction of the substrates.
However, the detailed studies by the inventors of the present invention proved that, when viewed diagonally, these conventional display elements have a certain viewing direction at which their display appears in blue or yellow. When viewed from such direction, the display quality of the display elements are significantly low. This indicates that these display elements are narrow in viewing angle. For example, the display elements are at a particular disadvantage when used as televisions or monitors of personal computers.
Moreover, in the Patent publication 1, it is described that an L-shaped (chevron shaped) electrode is used in order to improve the viewing angle property. However, the inventors of the present invention revealed that this arrangement described in the Patent publication 1 causes reduction in transmissivity and makes almost no improvement in viewing angle property.